1. Field of the Invention
The present invention relates to a display device in which a timing controller, a plurality of data driver ICs, a scanning line driving circuit and a display panel are provided separately. More particularly, the present invention relates to a display device, a data driver and a timing controller for conducting a multi gradation display by a voltage modulation method using a DA converter.
2. Description of the Related Art
Video signals of an image televised in an ordinary television broadcast are transmitted through a γ (gamma) correction which is consistent with IT (current-luminance) characteristics of a cathode ray tube (CRT). Accordingly, in the case of displaying the above video signals as an image in a display device other than the CRT, it is necessary to make a gradation correction (hereinafter referred to as γ correction) corresponding to the characteristics between the driving voltage and the luminance in the display device. This γ correction enables the luminance of a liquid crystal to be subjected to signal processing so as to be consistent with the level of original video signals initially generated, and allows precise reproduction of the contrast of an original image. In the case of a color screen, the above γ correction is also made for each of three primary colors individually so that fidelity reproduction of the hues of the original image is realized and color temperature setting and white balance adjustment are achieved by adjusting γ correction values. Meanwhile, data which was subjected to the γ correction has a tendency to increase the number of bit in comparison with the original data.
FIG. 1C is a graph showing V-T characteristics between a driving voltage and a luminance in a conventional liquid crystal panel. The vertical axis indicates the luminance (normalized, %), and horizontal axis indicates the data line driving signal (voltage). The characteristics between the driving voltage and the luminance in the liquid crystal panel are nonlinear as shown in FIG. 1C. Therefore, gradation data inputted as the video signals needs to be corrected as nonlinear driving voltages. In a general liquid crystal display device, they have been converted to analog voltages (driving voltages) by a nonlinear DA converter (DAC) in accordance with the characteristics between the driving voltage and the luminance in the liquid crystal panel. However, in recent years, liquid crystal display devices using a linear DAC (linear DA converter) for converting digital data to linear analog voltages as shown in FIG. 1B have been developed. Here, FIG. 1B is a graph showing conversion characteristics in the DAC in the conventional liquid crystal panel. The vertical axis indicates the data line driving signal (voltage), and horizontal axis indicates the output gradation signal (bit). In a liquid crystal display device using the linear DAC, gradation data is converted by using a look up table (LUT), and the converted data (hereinafter referred to as correction data) is subjected to DA conversion so as to obtain a driving voltage appropriate to the V-T characteristics. The correction data indicates nonlinear correction curves as shown in FIG. 1A so as to obtain the driving voltage in accordance with the V-T characteristics shown in FIG. 1C. Here, FIG. 1A is a graph showing correction curves indicated by the correction data in the conventional liquid crystal panel. The vertical axis indicates output gradation signal (bit) and the horizontal axis indicates input gradation signal (bit). Therefore, the digital data inputted to the LUT is required to be converted to the correction data with the large number of bit.
Japanese Laid-Open Patent Application JP-P2004-163946A discloses a display device for executing the γ correction by converting inputted digital gradation data to the correction data using the LUT. According to the display device disclosed in JP-P2004-163946A, the LUT is provided in a timing controller (TCON) for controlling a data line driving circuit which drives data lines on the display panel. The number of bit of the correction data converted by using the LUT becomes larger than the number of bit of the video signal inputted to the LUT, thereby the number of lines of a bus between the TCON and the data line driving circuit is increased in comparison with the number of lines of a bus between the TCON and an input source of the video signals. In the case of a serial transmission, the number of bit for the serial transmission is also increased, which results in high shift frequency.
Meanwhile, Japanese Laid-Open Patent Application JP-A-Heisei, 5-216430 discloses a liquid crystal display device for executing the gamma correction by installing the LUT in the data line driving circuit.
FIG. 2 is a block diagram showing the configuration of a liquid crystal display device according to the conventional technique. In this conventional technique, the LUT is installed in the data line driving circuit. Referring to FIG. 2, the liquid crystal display device according to the conventional technique includes a liquid crystal panel 11, a data line driving circuit 12, a scanning line driving circuit 13, and a timing controller (TCON) 14. The data line driving circuit 12 drives data lines on the liquid crystal panel 11. The scanning line driving circuit 13 drives scanning lines on the liquid crystal panel 11. The timing controller (TCON) 14 makes the liquid crystal panel 11 display images by controlling the data line driving circuit 12 and the scanning line driving circuit 13. The TCON 14 outputs an input gradation signal Dinj of 10 bits to data driver ICs 120l to 120n in the data line driving circuit 12 via a bus 17 on the basis of a video signal Din of 10 bits inputted from an outside. LUTs 121l to 121n respectively provided in the data drivers ICs 120l to 120n convert the input gradation signal Dinj into output gradation data Doutj of 12 bits, and output the output gradation data Doutj to latches 122l to 122n, respectively. Each of the latches 122l to 122n latches the output gradation data Doutj for the number of outputs of a driving signal D outputted from corresponding one of DACs 123l to 123n. Then, each of the latches 122l to 122n outputs the output gradation data Doutj to corresponding one of the DACs 123l to 123n in response to a latch signal 202 outputted from the TCON 14. Each of the DAC 123l to 123n conducts DA conversion for a signal Dout outputted from corresponding one of the latches 122l to 122n so as to drive the data lines on the liquid crystal panel 11.
The following fact has now been discovered. As the display device disclosed in of JP-P2004-163946A, in the liquid crystal display device incorporating the LUT inside the TCON, the number of lines in the bus between the TCON and the data line driving circuit becomes larger, which results in the circuit area to be expanded. In the case of serial transmission, shift frequency becomes higher that causes the increase in power consumption and EMI.
Meanwhile, the characteristics between the driving voltage and the luminance in a liquid crystal panel used for a liquid crystal display device are made different by manufacturers, individual panel properties, or usage environment such as temperatures and brightness. However, according to the display device described in JP-A-Heisei, 5-216430, since correction characteristics (correction curves) provided by the LUT are constant or can not be arbitrarily changed, it is required to prepare a data driver IC having specific characteristics in each liquid crystal panel. Furthermore, it is impossible to change characteristics of the LUT and DAC after preparing a chip. Therefore, in the case of causing a difference between the characteristics of a liquid crystal panel and that stored in the chip, particularly a difference with respect to characteristics (correction curves) that are made different in the respective colors (RGB) as shown in FIG. 1A, a fine adjustment can not be allowed for correcting the difference.